FIELD OF THE INVENTION
The invention relates to a control circuit for an MOS semiconductor component having a source side to which a load is connected in series, and a voltage source at fluctuating potential having a first terminal being connected through a first controllable switch to a gate terminal of the MOS semiconductor component and a second terminal being connected to the source terminal of the MOS semiconductor component.
Such control circuits are known and have been described by way of example in Published European Application No. 0 268 932B2.
Semiconductor components with a source-side load must be conductively controlled with a voltage that is higher than the drain voltage. That can be done with a voltage source connected to fluctuating potential, having potentials which increase as a function of the rise in the source potential in the course of the turn-on process of the MOS semiconductor component. Such voltage sources connected to fluctuating potential may be achieved, for instance, by a transformer coupling, a piezoelectric coupling or an optoelectric coupling. It is also possible to construct the voltage source that is at fluctuating potential by means of a bootstrap capacitor which, with the MOS semiconductor component blocked, is charged through a diode by a voltage source referred to ground. Circuitry problems can arise if that kind of control circuit is meant to be constructed to be compatible with a microcomputer. Those problems arise because the signals for the microcomputer are generally referred to a fixed potential and in particular to ground. The MOS semiconductor component is therefore typically likewise supplied with such a control signal through the transformer, piezoelectric converter or optocoupler.